1. Field of the Invention
This invention relates to a method and apparatus for operating a heater, such as a gaseous fuel fired water heater. This invention also relates to a water heater having two or more burner assemblies and a mounting apparatus for releasably attaching each burner assembly to a bottom wall of a combustion chamber, such as a water heater combustion chamber.
2. Description of Related Art
Many conventional water heater combustion chambers intentionally operate with a combustion chamber that is substantially sealed, except for communication with the surrounding environment through a flue stack and an inlet opening for fuel and/or air. In some designs, the combustion air is introduced into the combustion chamber through a restricted opening, wherein a portion of the air is mixed with fuel in the burner nozzle and ignited in a primary combustion region and the remaining portion of the air is directed around the burner to complete combustion. The remainder of the combustion chamber is substantially sealed. U.S. Pat. No. 5,797,355 describes such a gas-fired heater. The purpose of the restricted air opening in the combustion chamber is to prevent a combustion flame from passing from the combustion chamber to the ambient surroundings.
Alternatively, the heater may be constructed with a substantially sealed combustion chamber in which all or substantially all of the combustion air and fuel are directed through an inlet nozzle to the burner, denoted as a fully premixed or simply premixed burner, with the intent of improving burner and overall system performance. For example, U.S. Pat. No. 5,355,841 describes a gas-fired heater with a premixed burner having a substantially sealed combustion chamber. It is apparent that many conventional designs having premixed burner systems try to achieve a gas tight seal between the combustion chamber and a tank wall in order to limit the entry of secondary combustion air.
A common phenomenon associated with water heater designs employing premixed burners is an undesirable noise, upon ignition and during steady state operation of the combustion chamber. The noise is initiated by the transient pressure rise associated with burner ignition, and may persist during steady state operation if one or more frequencies generated by flame instabilities or other periodic energy input from the burners corresponds with one or more structural or fluidic natural frequencies of the water heater and if there is insufficient system damping to mitigate the acoustic response. Various approaches have been taken to provide noise reduction and/or pressure relief in the substantially sealed combustion chamber, as taught in U.S. Pat. Nos. 5,317,992, 5,435,716 and 5,791,298, including insulation provided on the interior of the combustion chamber, a diaphragm on the bottom of the combustion chamber, and openings in the combustion chamber covered by porous material or flaps. These approaches add to system cost and manufacturing complexity, and introduce additional components that can negatively impact reliability.
It is one object of this invention to provide a method and apparatus for operating a water heater wherein a pressure relief void is in communication with the combustion chamber, to relieve chamber pressure during ignition and also to prevent a combustion flame from passing through the pressure relief void during operational combustion.
It is another object of this invention to provide a gaseous fuel fired water heater that has two burner assemblies mounted within or exposed to a combustion chamber.
It is yet another object of this invention to provide a mounting apparatus for releasably attaching a burner assembly to a bottom wall or a base plate of a water heater combustion chamber.
The method and apparatus of this invention reduce undesirable noise associated with ignition and with steady state or operational combustion. The method and apparatus of this invention enhance design flexibility by providing a relatively broad range of port loading, the firing rate per square inch of burner material. The method and apparatus of this invention also enhance scale-up capabilities which allows one particular burner assembly design to be used in different operations with various load settings.
The above and other objects of this invention are accomplished with a method wherein a fuel and air mixture, preferably but not necessarily pre-mixed and containing sufficient air to completely combust the quantity of fuel, is introduced into a burner and burned or combusted within a combustion chamber. The fuel and air mixture is ignited within the combustion chamber. An exhaust flue forms communication between the combustion chamber and an ambient environment which surrounds the combustion apparatus. Combustion products discharge through the exhaust flue.
In a pre-combustion condition, the combustion chamber is filled with or houses a fluid, mostly air or another suitable oxidant. Upon initial ignition of the fuel and air mixture, a first portion of the pre-combustion fluid passes through a pressure relief void and a second portion of the pre-combustion fluid passes through the exhaust flue. Conventional water heater apparatuses having premixed burner systems try to seal the combustion chamber, except for communication with an air supply and the exhaust flue, which the prior art refers to as a substantially sealed chamber. According to this invention, the pressure relief void is intended to form a combustion chamber which is not substantially sealed.
In one embodiment of this invention, the pressure relief void is sized large enough to relieve an ignition pressure from the combustion chamber when the fuel and air mixture is initially ignited yet is sized small enough to prevent a combustion flame from passing through the pressure relief void during ignition and/or operational combustion of the continuously supplied fuel and air mixture.
The pressure relief void can have many different sizes, shapes, forms, and locations with the combustion chamber, as long as an effective area of the pressure relief void adequately relieves the ignition pressure and prevents the combustion flame from passing through the pressure relief void during ignition and/or operational combustion. For example, the pressure relief void can be formed by a peripheral gap between the combustion chamber wall and a vessel wall, such as of a water tank of the water heater. In other embodiments, the pressure relief void can be incorporated in the mounting structure for the pilot assembly or the bottom wall or side wall of the combustion chamber. Many different structural elements and configurations can be used to maintain or form the pressure relief void.
In one embodiment of this invention, the water heater apparatus has two or more burner assemblies mounted to a bottom wall of the combustion chamber. In one embodiment, two burner assemblies are positioned a distance apart from each other and form a catch area between the burner assemblies. The catch area is preferably but not necessarily located on the bottom wall, for catching debris fallout and/or condensation which may occur during combustion.
In another embodiment of this invention, each burner assembly preferably has a mounting apparatus for releasably attaching the burner assembly with respect to a bottom wall that at least partially defines the combustion chamber. The mounting apparatus includes a retainer which is secured, either fixedly or releasably, to the burner assembly. A clip is attached to the bottom wall. The clip has an end portion spaced from the bottom wall and thus forms a receiver. A portion of the retainer can be engaged within the receiver. Once engaged, a removable fastener can be used to fasten another end of the retainer against the bottom wall.
In one embodiment, the fastener is a screw. In another embodiment the fastener includes a catch or latch which can be removably engaged within a shoulder of the bottom wall. Any other suitable connecting device can be used to quickly attach and detach the burner assembly with respect to the bottom wall. The mounting apparatus of this invention simplifies field installation and/or maintenance of burner assemblies mounted within water heaters.